The present invention relates to a method of fabricating an abrupt hetero interface in the crystal growth of a chemical compound semiconductor multiple quantum well structure.
In the prior art, an example of this kind of technology is mentioned in the Journal of Crystal Growth Vol.107, pp. 567-572, "OMVPE growth of GaInAs/InP and GaInAs/GaInAsP quantum wells". In this reference (p.567, left column, line 21-p.569, left column, line 3, and FIG. 1), a method is indicated for growing an abrupt hetero interface comprising InP and InGaAs using an organometallic vapor growth technique.
When a InP/InGaAs interface having, for example, a multiple quantum well structure is formed by organometallic vapor growth, growth is interrupted for a short interval during the growth of the InGaAs layer and the growth of InP layer, or between growth of the InP layer and the growth of InGaAs layer, to allow valve switching and purge of residual gases in the growth chamber. At that time, P and As may separate from the growth layer surface or substitution from As to P may occur so that the quality of the hetero interface deteriorates. This is due to the fact that the vapor pressures of P and As, which are Group V elements, are high. It is thus important to prevent the separation of Group V elements and substitution so as to improve the quality of the hetero interface.
The method for fabricating a InGaAs/InP hetero interface by growing a InGaAs layer on a InP layer given in the aforesaid reference, is described below. FIG. 1 is a diagram showing a timing at which a source gas is switched over in the conventional process for fabricating a hetero interface disclosed in the above reference.
Firstly, trimethylindium (TMIn) and phosphine (PH.sub.3) are supplied to a growth chamber, and a InP layer is grown. Immediately after growth of the InP layer, supply of TMIn is stopped, and passage of PH.sub.3 is continued for t1 seconds to purge TMIn from the growth chamber. The source gas is then switched from PH.sub.3 gas to arsine (AsH.sub.3) gas, and AsH.sub.3 gas is supplied to the growth chamber for t2 seconds. After T2 seconds, TMIn and triethylgallium (TEGa) are supplied to the growth chamber, and a InGaAs layer is grown. t1 and T2 are growth interruption intervals. The optimum intervals are calculated to be t1=T2=0.5 seconds. When fabricating a InP/InGaAs hetero interface, the times for which arsine and phosphine are supplied are reversed, but the same method and times are used.
However, if a InGaAsP layer was grown on a InGaAs layer or a InGaAs layer was grown on a InGaAsP layer when the growth interruption condition shown above was t1=t2=0.5 seconds, for example, a substitution from As to P occurred on the InGaAs surface for t1 seconds causing a deterioration of the hetero interface.